1. Field of the Invention
This invention relates to a recording method and apparatus which makes it possible to improve an image quality and throughput, and more particularly to an ink jet recording apparatus and its method wherein characteristics of temperature sensors can be obtained precisely in a short time.
2. Related Background Art
Recording apparatuses, such as a printer, a copying machine, and a facsimile, each have a configuration to form an image consisting of dot patterns on a recording medium such as a sheet of paper and a plastic sheet on the basis of image information.
The recording apparatuses can be classified into ink jet type, wire dot matrix type, thermal type, and laser beam type apparatuses according to their respective recording methods. The ink jet type apparatus (an ink jet recording apparatus) among them has a configuration in which ink droplets (recording droplets) are ejected and sprayed from ejection outlets of its recording heads so as to be deposited on the recording medium in recording.
Recently, a lot of types of recording apparatuses are used. They are, however, required to provide high-speed recording, high resolution, quality images, and lower noises. The above ink jet recording apparatus can satisfy these requirements. Among them there is an ink jet recording apparatus in which heat energy is given to ink in a nozzle to cause bubbles, so that the ink is ejected from the recording head by the expansion force for recording. Temperature management of the recording head is very important to stabilize the ink ejection and the ejection quantity necessary to satisfy the above requirements.
Therefore, in the conventional ink jet recording apparatuses, there has been used a procedure for controlling temperatures of recording heads so as to be within a required range on the basis of recording head temperatures detected by a so-called closed loop method in which a head temperature is detected by a temperature detecting means fit to a recording head portion or by a temperature calculation method in which a head temperature history is presumed by calculation from energy applied to the head, or by both methods.
As an example of a correction procedure for the above temperature detecting method, in Japanese Patent Application Laid-open No. 5-31906, values used for calculation (for example, tables) are corrected by using a difference between a temperature detected in a thermally stabilized status by the temperature detecting means on the recording head and the calculated temperature presumed by calculation. In Japanese Patent Application Laid-open No. 5-31918, a temperature detected by the temperature detecting means on the recording head is corrected with reference to a temperature detected by an ambient temperature detecting means incorporated in the main unit of the recording apparatus, when recording is not performed or at a timing when the temperature is not changed. Further, in Japanese Patent Application Laid-open No. 5-64890, a caluculated temperatue is corrected by using a ratio of the temperature detected by the temperature detecting means on the recording head to the above calculated temperature. These methods are used for correcting head characteristics such as a variation in the above temperature detecting means, differences between thermal time constants or those between thermal efficiencies at ink ejection in respective recording heads which are difficulties existent in replacement type recording heads.
In the above temperature calculation method, generally, temperature behavior (temperature raise) of an object is previously obtained, in respect to the downward movement of the object temperature at unit time intervals after the temperature raise caused by applied energy at unit time intervals, and then calculation is made to obtain the total sum of a difference between the current object temperature and the past temperature which has been raised at unit time intervals to presume the present object temperature.
A heater used for the temperature control is a heater member for heating joined to the recording head portion or a heater for ink ejection in an ink jet type recording apparatus which forms sprayed droplets by utilizing thermal energy for recording, in other words, means for ejecting ink droplets by utilizing expansion of bubbles due to boiling of an ink film. If the ink ejection heater is used, it is energized to an extent that bubbles are not expanded.
As mentioned above, the temperature management of the recording heads is important to allow the ink jet recording apparatus to effect stable ink ejection, therefore, it is intended to obtain temperatures of the recording heads precisely in various methods. However, if temperatures of recording heads are to be detected by temperature detecting means added to the recording heads, for example, if temperatures are to be detected by using temperature dependencies of output voltages of diode sensors, an offset (a variation of output values at the same temperature) has a substantial variation between respective sensors, though a proportional coefficient (hereinafter referred to "inclination") of a temperature-output voltage does not have any substantial variation between respective sensors (for the head temperature management). Accordingly, the head temperature as an absolute value cannot be obtained only from the same output voltage, unless characteristics (rank) of a Di sensor is acquired.
Therefore, the above rank is measured previously, for example, at manufacturing a recording head, and then the head is notched in association with rank values which have been measured or rank values that are previously stored in an EEPROM or other memories. It provides precise correction of the recording head temperatures if the rank values are read when the main unit is installed. If diode rank values are stored in the recording heads, however, it takes much time and labor to store them and a lot of cost since a storing means (for example, ROM) is needed for each recording head. In addition, in a method of detecting the diode ranks by utilizing combination of contacts for diode rank values made on the recording heads, there have been difficulties such as large-sized apparatuses and higher cost since it requires the contacts and wiring for reading by the amount of information.
Accordingly it can be considered as a method to solve the problems that the recording apparatus main unit is used to measure the diode ranks of the recording heads. More specifically, it is a method in which correction is made so that a thermistor temperature matches the diode sensor temperature when the temperature value of the thermistor in the main unit is considered to be the same as the recording head temperature.
However, when a new recording head is mounted on the main unit, conventionally the new recording head may have been left in an environment different from that of the main unit, in other words, in an environment whose temperature is extremely different from that of an environment in which the main unit is installed, such as in a warehouse cold in winter or in a car hot in summer, which is an extreme case.
If so, as described in the above, it needs a substantial waiting time after the recording head is mounted on the main unit to measure the diode rank. In addition, if the diode rank is measured without the waiting time, the measurement error of the rank value may be too big to obtain the recording head temperature precisely. The method has a difficulty that it sometimes leads to a failure of stabilization in the ink ejection from the recording head or in the amount of the ink ejection.